1. Field of the Invention
This invention relates generally to the field of semiconductor device manufacturing and, more particularly, to a method and apparatus for using a dynamic control model to compensate for a process interrupt.
2. Description of the Related Art
There is a constant drive within the semiconductor industry to increase the quality, reliability and throughput of integrated circuit devices, e.g., microprocessors, memory devices, and the like. This drive is fueled by consumer demands for higher quality computers and electronic devices that operate more reliably. These demands have resulted in a continual improvement in the manufacture of semiconductor devices, e.g., transistors, as well as in the manufacture of integrated circuit devices incorporating such transistors. Additionally, reducing the defects in the manufacture of the components of a typical transistor also lowers the overall cost per transistor as well as the cost of integrated circuit devices incorporating such transistors.
Generally, a set of processing steps is performed on a lot of wafers using a variety of processing tools, including photolithography steppers, etch tools, deposition tools, polishing tools, rapid thermal processing tools, implantation tools, etc. The technologies underlying semiconductor processing tools have attracted increased attention over the last several years, resulting in substantial refinements. However, despite the advances made in this area, many of the processing tools that are currently commercially available suffer certain deficiencies. In particular, such tools often lack advanced process data monitoring capabilities, such as the ability to provide historical parametric data in a user-friendly format, as well as event logging, real-time graphical display of both current processing parameters and the processing parameters of the entire run, and remote, i.e., local site and worldwide, monitoring. These deficiencies can engender non-optimal control of critical processing parameters, such as throughput, accuracy, stability and repeatability, processing temperatures, mechanical tool parameters, and the like. This variability manifests itself as within-run disparities, run-to-run disparities and tool-to-tool disparities that can propagate into deviations in product quality and performance, whereas an ideal monitoring and diagnostics system for such tools would provide a means of monitoring this variability, as well as providing means for optimizing control of critical parameters.
One technique for improving the operation of a semiconductor processing line includes using a factory wide control system to automatically control the operation of the various processing tools. The manufacturing tools communicate with a manufacturing framework or a network of processing modules. Each manufacturing tool is generally connected to an equipment interface. The equipment interface is connected to a machine interface which facilitates communications between the manufacturing tool and the manufacturing framework. The machine interface can generally be part of an advanced process control (APC) system. The APC system initiates a control script based upon a manufacturing model, which can be a software program that automatically retrieves the data needed to execute a manufacturing process. Often, semiconductor devices are staged through multiple manufacturing tools for multiple processes, generating data relating to the quality of the processed semiconductor devices.
During the fabrication process various events may take place that affect the performance of the devices being fabricated. That is, variations in the fabrication process steps result in device performance variations. Factors, such as feature critical dimensions, doping levels, contact resistance, particle contamination, etc., all may potentially affect the end performance of the device. Various tools in the processing line are controlled in accordance with performance models to reduce processing variation. Commonly controlled tools include photolithography steppers, polishing tools, etching tools, and deposition tools. Pre-processing and/or post-processing metrology data is supplied to process controllers for the tools. Operating recipe parameters, such as processing time, are calculated by the process controllers based on the performance model and the metrology information to attempt to achieve post-processing results as close to a target value as possible. Reducing variation in this manner leads to increased throughput, reduced cost, higher device performance, etc., all of which equate to increased profitability.
Typically, the control models used to generate the operating recipe parameters for the tool are xe2x80x9csteady-statexe2x80x9d models. For example, models used to control a polish or etch process control the processing time assume that the average rate is constant throughout the processing run. In the actual processing run of the tool, the processing rate is not actually constant. A typical processing run may include different segments, such as a warm-up segment and one or more main segments. The actual processing rate may vary between each of these segments and even within each segment.
The processing rate changes during the course of the processing run for a variety of reasons. For a polish process, the rate is dependent on the topography of the wafer surface. As the wafer is planarized, the rate approaches the xe2x80x9cbare-waferxe2x80x9d removal rate. In addition, multiple polishing recipe segments may have different polishing rates themselves. For example, a commonly used polishing technique for polishing a copper layer to form interconnect structures uses two stages. The first polishing stage (i.e., platen 1) removes the copper at a relatively high rate. The first stage removes most of the copper extending beyond interconnect trenches formed in an interlayer dielectric (ILD) layer. The second polishing stage (i.e., platen 2) removes the copper at a much slower rate until an endpoint signal is received. A typical endpoint signal may be generated optically based on the optical property differences between the copper and an underlying barrier layer. After an endpoint signal is received, the polishing continues for a fixed amount of time (i.e., overpolish time) to help ensure that all of the copper is removed. Variations in the incoming thickness of the copper layer can introduce processing variations in the tool that can cause excessive dishing of the copper or erosion of the barrier layer and ILD layer. For example, if the incoming copper thickness is sufficiently small, all of the copper may be removed during the platen 1 polish. Subsequent platen 2 polishing will cause high degrees of dishing or erosion. If the incoming copper thickness is sufficiently high, a large amount of copper will still remain after the platen 1 polish, resulting in an extremely long platen 2 polish time.
One possible control technique for controlling the polishing tool is to control the platen 1 polish time based on incoming copper thickness to try to provide a constant remaining copper thickness for the platen 2 polish. Controlling the tool in this manner will result in an endpoint time for the platen 2 polish that is reasonably stable. Such a control technique assumes a steady state material removal rate for determining the operating recipe parameter for the platen 1 polishing time.
An etch process may also include similar processing rate variations within the etching segments. During an etch process, material can build up inside the chamber, reducing the etch rate. Also, changes in the power settings and reactant gas concentrations that are used throughout the run may cause variations in the etch rate. An exemplary control technique may involve controlling the etch time for one or more segments of the processing run based on the incoming thickness of a process layer to be etched to reduce the amount of overetch. Overetching has the potential to change the critical dimensions of the features being etched or to damage surrounding features and degrade the performance of the semiconductor device. In controlling the etch time to minimize overetch time, an average etch rate of the etch tool may be used to predict an etch time based on the incoming process layer thickness.
Steady state control techniques assume a constant or average processing rate and control the processing time in one of the segments of the processing run to achieve an end product characteristic that is presumably closer to a target value. Under normal circumstances, this steady state approach is acceptable. Controlling the operating recipe parameters based on the average processing rate factors in the processing rate variations in the multiple segments.
However, some processing runs are interrupted for various reasons, such as tool problems, including loss of power, operator abort, or loss of gas pressure, etc. Sometimes the error that caused the interruption of the processing run also causes a change in the assumed processing rate of the tool. For example, if the plasma power in an etch tool is higher than expected, the tool may be shut down. The increased plasma power may have resulted in a higher than expected etch rate for the tool. In such cases where the processing run is interrupted, a steady state model cannot be employed to generate operating recipe parameters for completing the processing of the wafer upon recommencement of the processing run. The steady state model factors in the processing rate variations inherent in the processing run and generates a total processing time. The predicted processing time is only valid for wafers subjected to a complete processing run. Because a wafer being processed after an interruption is not subjected to a complete processing run, the steady state condition is not present, and the steady state control model may not be used to control the operating recipe parameters of the tool.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
One aspect of the present invention is seen in a method for processing an interrupted workpiece. The method includes providing a dynamic control model defining the processing characteristics of a processing tool throughout a processing run; providing a partially processed workpiece; determining an extent of processing metric for the partially processed workpiece; and determining at least one operating recipe parameter of the processing tool based on the dynamic control model and the extent of processing metric.
Another aspect of the present invention is seen in a manufacturing system including a processing tool and a process controller. The processing tool is adapted to process a partially processed workpiece in accordance with an operating recipe. The process controller is adapted to determine an extent of processing metric for the partially processed workpiece and determine at least one parameter of the operating recipe based on a dynamic control model defining the processing characteristics of the processing tool throughout a processing run and the extent of processing metric.